The term “Flettner rotor” is to be understood here as a rotary cylinder utilizing a Magnus effect. The Magnus effect causes formation of a lift acting on a rotating cylinder when it is located in a stream of air, said lift acting perpendicularly to the direction of this stream.
From a publication DE102005001235A1 there is known a Horizontal Axis Wind Turbine (HAWT) having axis of rotation substantially parallel to the wind direction, with Flettner rotors, namely a Flettner windmill. Generating by the rotor a force oriented perpendicularly to the wind direction and to the rotor axis —as a result of pressure difference on the sides of the rotor (Magnus effect) is known and used in the art, mainly to drive ships.
There is also known from the publication WO2007/076825 a VAWT with Flettner rotors, which on the leeward side of the turbine rotate in different direction than on the windward side.
There are also known other similar solutions, in which Flettner rotors do not rotate on the leeward side or are covered then by special covering elements, which move on special trolleys (publication DE000004033078A1) or where a special mechanism turns the rotors by 180° (according to publication DE102010026706A1).
Another known solution according to publication DE 102010008061 A1 (US2011/0198857A1) comprises rotors moving along a plane tilted with respect to the horizontal line and returning on the leeward side on bearings attached to a toothed belt. A spinning motion of rotors is provided by a non-moving toothed belt, on which gears mounted on the rotors axles roll.
There are also known wind turbines with Flettner rotors of axes substantially parallel to the turbine rotation axis, arranged within a rotary body of the turbine, which turbines have inner cylinder arranged between Flettner rotors, wherein said inner cylinder rotates in the direction opposite to direction of rotation of said rotary body. However, in these turbines the inner cylinder acts as a support, and the distance between the inner cylinder and the Flettner rotors is relatively large, therefore the rotation of the inner cylinder does not affect the pressure difference on the sides of the rotors. Turbines of this type are known from publications JP2008175070, WO2007076825, BE898634.
It would be advisable to further improve the construction of wind turbines with use of Flettner rotors.